The present invention relates to torque motors or motors of the type wherein the shaft is rotated by an amount less than one-half revolution in either direction from a center position. Torque motors are typically employed for rotary actuation of a device to be electrically controlled, as for example a servo motor rotary valve. Torque motors capable of operating on relatively low voltage direct current power have been found particularly suitable for actuating valve applications such as the air throttle valve of an internal combustion engine and particularly throttle valves for engines in motor vehicles.
In motor vehicle air throttle applications, it is necessary that a torque motor employed for rotating the throttle shaft against the force of the throttle return spring provide substantial torque at a relatively low wattage in view of the low voltage available on board typically twelve to twenty-four volts DC. Furthermore it is desired that the mass and volume of the torque motor be minimized to facilitate mounting on the air throttle body to reduce the inertial loading from vibration induced by engine operation and jounce from vehicle movement. Heretofore, known torque motors for vehicle air throttle applications have been bulky, heavy and difficult to assemble and mount on the air throttle and thus relatively costly in high volume mass production of vehicle engines.
Accordingly, it has been desired to provide a relatively low wattage torque motor operating from a low voltage direct current supply such as encountered on board a motor vehicle and one which has a relatively low mass and reduced volume with a relatively high torque output for the power available for the motor.